Traveling nut assembly with low friction and automatic brake

ABSTRACT

A low friction traveling nut assembly carried on a threaded spindle for linear movement therealong in response to rotation of the spindle about its rotational axis includes a housing, a roller rotatably mounted within the housing by roller bearings, and a clutch mechanism which engages when the spindle is rotated in one direction relative to the traveling nut assembly to effect substantial sliding friction between the roller and a bearing surface reacting with the housing so that the traveling nut assembly is automatically braked to resist movement in one axial direction.

The invention relates to a traveling nut assembly having low frictionand an automatic brake in which rolling friction or sliding friction canbe selectively achieved between the components forming the nut. In orderto develop a lifting and lowering movement, the nut works jointly with athreaded drive spindle. The invention is particularly suited forutilization in mechanisms lifting loads, such as elevating platforms forautomotive vehicles.

In designing such a spindle-type elevating platform for automotivevehicles, two conflicting objectives are encountered. One the one hand,low friction forces and high efficiency between the spindle and nutshould exist so that the necessary drive power and the stress on thecomponents may be kept low. On the other hand, high friction forces andlow efficiency between the spindle and the nut should exist so thatautomatic braking is present to hold the load lifted in any positionwithout the necessity of an additional brake.

In the well-known spindle-type elevating platforms with a conventionalsplit traveling nut, only the second of these objectives is met. Aspindle-type elevating platform employing a planetary-type roller nut ofspecial design provides low friction, but an additional brake is needed.Traveling elements are known where the lift motion is carried out by anut having reduced friction and the lowering motion is carried out by acut nut. However, such an arrangement is expensive and has thedisadvantage that two traveling elements have to be supervised forreasons of safety.

It is, therefore, a principal object of the invention to provide africtionless traveling nut in which the two aforementioned objectivesare fulfilled optimally by a single nut of simple construction.

In order to obtain automatic braking in one direction, the traveling nutis designed so that rolling friction between individual components canbe selectively replaced or supplemented by sliding friction. Rollingfriction generates a smaller force than does sliding friction under asimilar load. In a traveling nut assembly embodying the inventionherein, sliding friction between the components generates a sufficientforce to prevent automatic lowering of the load, a braking forcesubstantially equivalent to that encountered if a friction nut wereemployed. Disposed between one component mounted in a sliding bearingand another component moving relative to the first-named component underrolling friction, a roller-type locking mechanism is appropriatelyarranged and is dependent on the direction in which the nut is moved sothat the rolling friction can be changed over to sliding friction andvice versa.

According to a preferred embodiment, the nut is designed as a planetaryroller nut in which a clutch is provided on at least one of theplanetary rollers. In order to achieve compact construction, theplanetary rollers are rotatably mounted on axles by suitable rollersbearings and the axles in turn, are rotatably positioned in the housingof the nut to react against a sliding bearing. The clutch is arrangedbetween a planetary roller and its respective axle.

In an alternative design, the clutch can be arranged on a shaft or axlerigidly connected with the roller. The clutch is surrounded by anannular component which is rotatable in the nut housing under slidingfriction.

FIG. 1 is a partial cross-sectional view of the traveling nut assemblyconstructed according to the invention illustrating the automaticbraking mechanism; and

FIG. 2 is a fragmentary, partial cross-sectional view of an alternativeembodiment of the traveling nut assembly.

The traveling nut assembly is a planetary roller nut incorporating aone-way clutch or back pedal brake. The traveling nut includes a housing2 having axial openings through which a threaded drive spindle 1 havinga V-thread extends. An cylindrical axle 3 is mounted within the housing2 on an axis parallel to the elongate axis of the spindle 1. Journaledon the axle 3 is a planetary roller 8 which cooperatively engages thethreaded drive spindle 1. Preferably, the traveling nut assembly hasthree or more such rollers and axles, each being equally spaced aboutthe periphery of the spindle.

The axle 3 is supported for rotation within the housing 2 at each end bya pair of annular sliding bearings 5 in the radial direction and by apair of spherical bearings 9 in the axial direction.

The planetary roller 8 has a central bore through which the axle 3extends, the axle 3 extending axially outward beyond each end thereof.The bore has a diameter greater than the axle 3 so that a space isdefined therebetween. Spaced radial roller bearings 4 positioned withinthe space rotatably mount the planetary roller 8 on the axle 3 to permitrelatively friction free rotation.

An axial roller bearing 7 is disposed between the upper surface of theplanetary roller 8 and the inner surface of the top of the housing 2. Aload acting on the housing 2 is transferred to the planetary roller 8through the roller bearing 7. When the traveling nut is mounted forrotation upon the threaded drive spindle 1, the traveling nut will movelinearly thereon in response to rotation of the spindle 1. If thespindle 1 is rotated counterclockwise on its elongate axis, thetraveling nut will move along the spindle threads upwardly. If thespindle 1 is rotated clockwise, the traveling nut will move downwardly.

Positioned within the space defined by the axle 3 and the planetaryroller 8 between the spaced roller bearings 4 is a clutch 6, a freewheeling hub with a back pedal brake. The one-way clutch 6 is engaged,when the spindle 1 is rotated clockwise, so that the planetary roller 8and the axle 3 are locked together so as to prevent relative rotationalmovement therebetween. During the counterclockwise rotation of thespindle 1 causing the traveling nut to move upwardly, braking action isreleased so that the planetary roller 8 can freely rotate about the axle3. The clutch 6 can be designed in a conventional manner. For example, alocking roller mechanism might be employed. Needle bearing roller bodiesmay be employed as a housing for the clutch 6.

The sliding bearings 5 on both ends of the axle 3 are constructed sothat the sliding friction between the respective surfaces is relativelygreat when the axle 3 rotates to generate the braking force necessaryfor automatic braking of the traveling nut. This braking force preventsthe traveling nut from moving downward until the spindle 1 is rotated toovercome this force. If the traveling nut is moved upward, the axle 3does not rotate in the bearings 5 because of the sliding friction;however, the clutch 6 is released so that the sleeve-shaped planetaryroller 8 rotates about the roller bearings 4 with rolling frictionexisting on all functioning bearing points. The axle 3 is rotated onlywhen the clutch 6 is engaged as nut is lowered.

Because of the V-thread on the spindle 1 and the inherent angle of thethread, the planetary rollers 8 are pushed radially outward when a loadacts on the traveling nut. As a result, the axle 3 in the slidingbearings 5 is pushed radially outward. If the sliding bearings 5 areworn, the axle 3 moves radially outwardly until it is no longer inengagement with the spindle 1. As a safeguard, a follow-up safety nut,such as an ordinary cut nut (not shown), is provided to run along withthe traveling nut. Since the safety nut will not normally be subjectedto a load, all functions of the traveling nut can be supervised withoutsubstantial additional frictional forces.

According to another embodiment which is not shown, shafts or axles arefixed to and extend axially from both ends of the planetary roller. Theplanetary roller and axle can be constructed integrally if desired.Here, in addition to the radial roller bearing, a one-way clutch isarranged on this fixed shaft and is connected with an annular componentwhich is rotatably disposed within the housing of the traveling nutunder sliding friction. With a V-thread on the spindle 1, the one-wayclutch in such a construction is appropriately arranged on the outerperiphery of the fixed shaft so that the planetary roller can moveradially outward when the sliding bearings are worn similar to theembodiment of FIG. 1.

The clutch 6 can cooperate with a radial bearing or with an axialbearing 11 as illustrated in FIG. 2. The axial bearing surface 11 isprovided between the axle 3 or a corresponding bearing pivot of theplanetary roller 8 according to the embodiment shown in FIG. 2. Thisbearing surface 11 extends transversely to the direction of the axle 3.The sliding friction required for the generation of the braking forceoccurs on this bearing surface as soon as the clutch 6 interrupts therolling friction between the components. Here, the load acting on thehousing 2 of the traveling nut would bear on this axial sliding bearingsurface 11. Such a construction has the advantage that there does nothave to exist any force acting on the planetary roller 8 radiallyoutward in order to produce the bearing pressure on the sliding bearing11. As a result, a trapezoidal thread can be provided on the threadedspindle 1. In case of wear at the axial sliding bearing surface 11, theplanetary roller 8 merely is axially shifted slightly relative to thehousing 2.

As seen in FIG. 2, the upper spherical bearing is replaced by the axialsliding bearing 11. The axle 3 has a widened head portion 10 on itsupper end on which the housing 2 of the nut rests by way of the slidingbearing 11. The head portion 10 is supported on an axial roller bearing7 which transfers the load to the planetary roller 8. The slidingsurface 12 on the head portion 10 can be made annular in order todeliver the required braking force. If the one-way clutch 6 is engagedduring the lowering motion of the traveling nut to lock the axle 3 andthe roller 8 together, sliding friction occurs between the annularsurface 12 and the sliding bearing 11.

To position the axle 3 radially, a shoulder on the housing 2 is providedagainst which head portion 10 of the axle 3 bears. An appropriate radialroller bearing may be provided for this purpose. If necessary, the axialsliding bearing 11 can be employed along with a radial sliding bearing 5as shown in FIG. 1. In the construction shown in FIG. 2, the lower endof the axle 3 can be placed in the housing 2 in any desired way toprovide rolling friction or sliding friction.

I claim:
 1. A traveling nut assembly carried on a threaded spindle forlinear movement therealong in response to rotation of the spindle aboutits rotational axis, the traveling nut assembly comprising:a housingthrough which the spindle extends; a roller within said housing having alow friction mounting and operatively engaging the spindle; bearingmeans carried by said housing; and clutch means responsive to rotationof said roller for selectively effecting frictional engagement betweensaid roller and said bearing means, said clutch means being engaged whenthe spindle is rotated in one direction so that sliding friction betweensaid roller and said bearing means provides increased resistance toaxial movement of the traveling nut on the spindle, said clutch meansbeing disengaged when the spindle is rotated in the other direction sothat said roller rotates without substantial resistance.
 2. A travelingnut assembly carried on a threaded spindle for linear movementtherealong in response to rotation of the spindle about its rotationalaxis, the traveling nut assembly comprising:a housing through which thespindle extends; an axle rotatably mounted within said housing spacedfrom the spindle; first bearing means carried by said housing forfrictionally reacting with said axle to oppose rotation of said axlerelative to said housing; a roller operatively engaging the spindle andhaving a bore through which said axle extends; second bearing means forrotatably mounting said roller on said axle and providing substantiallyfriction free rotation of said roller thereabout; and clutch means forselectively locking said roller to said axle, said clutch means beingengaged when the spindle is rotated in one direction so that slidingfriction between said axle and said first bearing means providesincreased resistance to axial movement of the traveling nut on thespindle, said clutch means being disengaged when the spindle is rotatedin the other direction so that said roller rotates about said axlewithout substantial resistance.
 3. The traveling nut assembly of claim 2wherein said clutch means is a locking roller mechanism.
 4. Thetraveling nut assembly of claim 2 wherein said bore and said axle havecircular cross sections, at least a portion of said bore having adiameter greater than said axle so as to define an annular space betweensaid axle and said roller, and said clutch means being disposed withinthe space between said axle and said roller.
 5. The traveling nutassembly of claim 4 wherein said second bearing means is a rollerbearing disposed within the space between said axle and said roller. 6.The traveling nut assembly of claim 5 further including a second rollerbearing disposed within the space between said axle and said rollerremote from the first-named roller bearing, said clutch means beingdisposed between said roller bearings.
 7. The traveling nut assembly ofclaim 2 wherein said axle extends beyond the opposite ends of theroller, said first bearing means rotatably mounting at least one end ofsaid axle, the surface of said axle sliding relative to the surface ofsaid first bearing means.
 8. The traveling nut assembly of claim 7wherein said first bearing means is annularly disposed about thecircumferential surface of said axle and provides a radial load bearingsuface.
 9. The traveling nut assembly of claim 8 wherein the oppositeends of said axle are each mounted within a radial load bearing surfaceat the respective ends of said housing.
 10. The traveling nut assemblyof claim 2 wherein said first bearing means is positioned at one end ofsaid axle, a load on said housing causing frictional engagement in anaxial direction between the axial end of said axle and said firstbearing means.
 11. The traveling nut assembly of claim 2 wherein saidtraveling nut assembly is a planetary roller nut with a plurality ofrollers mounted on an equal number of axles, clutch means being providedfor at least one of the axle and roller subassemblies.